Network monitoring script in Bash Scripting - Step-by-Step Execution

Concept Flow - Network monitoring script

Start script

↓

Ping target IP

↓

Check ping result

↓

Log success

↓

Wait for interval

↓

Repeat or Exit

The script pings a target IP, checks if it is reachable, logs the result, waits for a set time, and repeats.

Execution Sample

Bash Scripting

#!/bin/bash
TARGET=8.8.8.8
while true; do
  ping -c 1 $TARGET > /dev/null
  if [ $? -eq 0 ]; then
    echo "Host is up"
  else
    echo "Host is down"
  fi
  sleep 5
done

This script continuously pings the target IP 8.8.8.8 every 5 seconds and prints if the host is up or down.

Execution Table

Step	Action	Ping Command Result	Condition Check	Output	Next Step
1	Ping 8.8.8.8 once	Success (exit code 0)	0 == 0	Host is up	Sleep 5 seconds
2	Wait 5 seconds	N/A	N/A	N/A	Repeat ping
3	Ping 8.8.8.8 once	Fail (exit code 1)	1 == 0 is false	Host is down	Sleep 5 seconds
4	Wait 5 seconds	N/A	N/A	N/A	Repeat ping
...	Loop continues	...	...	...	...
Exit	User stops script	N/A	N/A	Script ends	Stop

💡 Script runs indefinitely until user stops it manually.

Variable Tracker

Variable	Start	After Step 1	After Step 3	Final
TARGET	8.8.8.8	8.8.8.8	8.8.8.8	8.8.8.8
Ping exit code	N/A	0 (success)	1 (fail)	Varies each ping

Key Moments - 3 Insights

Why does the script use 'ping -c 1' instead of just 'ping'?

Using 'ping -c 1' sends only one ping packet per check, so the script can quickly determine if the host is reachable without waiting for multiple pings. This is shown in execution_table step 1.

What does the '$?' variable represent in the script?

'$?' holds the exit code of the last command, here the ping. A zero means success (host reachable), non-zero means failure. This is checked in the condition at step 1 and 3 in the execution_table.

Why is there a 'sleep 5' command after each ping?

The 'sleep 5' pauses the script for 5 seconds to avoid flooding the network with pings and to space out checks. This is the 'Wait 5 seconds' action in steps 2 and 4.

Visual Quiz - 3 Questions

Look at the execution table, what is the output when the ping command exit code is 0?

A Host is up

B Host is down

C Ping failed

D No output

💡 Hint

Check the 'Output' column in step 1 of the execution_table where ping exit code is 0.

At which step does the script wait before repeating the ping?

A Step 1

B Step 3

C Step 2

D Step 4

💡 Hint

Look for 'Wait 5 seconds' in the 'Action' column of the execution_table.

If the ping command always fails, what will be the output at step 3?

A Host is up

B Host is down

C No output

D Script exits

💡 Hint

Refer to step 3 in execution_table where ping fails and output is shown.

Concept Snapshot

Network monitoring script in bash:
- Use 'ping -c 1 <IP>' to send one ping
- Check exit code with '$?'
- If 0, host is reachable; else unreachable
- Log result with echo
- Use 'sleep <seconds>' to wait between checks
- Loop with 'while true' for continuous monitoring

Full Transcript

This network monitoring script uses a loop to ping a target IP address once every 5 seconds. It checks the exit code of the ping command to determine if the host is reachable. If the exit code is zero, it prints 'Host is up'; otherwise, it prints 'Host is down'. The script then waits 5 seconds before repeating the check. This cycle continues indefinitely until the user stops the script manually.